Electrolytic cells

ABSTRACT

An electrolysis cell having rotating, disc-form cathodes immersed in an electrolyte. Sheet form anodes are disposed between the cathodes. Means are provided for advancing the anodes to compensate for dissolving of the anodes during electrolysis.

[56] References Cited UNITED STATES PATENTS 526.482 9/1894 Bridgman..................... 2,046,467 7/1936 Krause Wilhelm-plat: l. Wilhelm Eisenbach, Mulheim-Ruhr, Lembkestabe 6, both of Germany United States Patent [72] inventors Karl Ziegler; Mulheim-Ruhr, Kaiser- WS m m m m m u e mT.m .m m M m c m r 3 as N m Mm MHma V noem "R GM R G h 0 0D 9 46 5 r 99 9 H H H.ni 32 1 mm a m J 77 3 63 4 .l UM 47 6 al- 32 8 mi 7 n m 23 PA M m E m v. 8H 7 4. M yd 9 n 6 4 1 Ml Zlm- QLV. w 7ON GP 0. dc mm fimfi AHPAP 111111] 25323 2247333 .lllllll Anorney- Burgess, Dinklage & Sprung [54] ELECTROLYTIC CELLS 24 Claims, 6 Drawing Figs.

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L liiii SHEET 1 BF 4 kflRL ZIEGLIR wz'mnm Um INVENTORI FIG.2

PATENTEDNUV 15 ml ELECTROLYTIC csus This invention relates to electrolytic cells. In particular, it relates to cells which have sheet form anodes which are replaced as they are dissolved.

An article in Chemie-lngenieur-Technik 35 (I963) 330 describes, inter alia, an electrolytic cell in which metal alkyls, in particular lead tetraethyl, can be produced by electrolysis. This electrolysis uses metal anodes, preferably of lead, a complex organometallic electrolyte and rotating disc-form cathodes which are wetted with mercury. This cell, which was of a relatively small scale, was run at a maximum of 200 a., distributed among three anodes and four rotating disc cathodes. The lead anodes wen-e 4 mm. thick, and these were interposed between the rotating disc cathodes which were spaced 9 mm. apart. Hence, at the beginning of electrolysis, the electrolyte gap between the electrodes was 2.5 mm., which widened to 4.5 mm. just before the anodes dissolved. The anodes corresponded in shape to the effective part of the rotating circular cathodes.

If this cell is run at a constant voltage of, e.g. 4.5 volts, the intensity of the cross section, from an individual anode decreases from 67 a. at the start, to 37 a. just before complete dissolution, for an initial current density of 36 a./dm. If it were desired to run the cell at a constant current intensity, the voltage would have to be increased accordingly. In this known cell, it was possible by using a mechanical dodge to ensure that, when working with a substantially constant voltage, the average current absorption throughout the cell also remained substantially constant. This was achieved by initially inserting only one metal anode and introducing the other two anodes at intervals of one hour. Since the anodes dissolved completely in about three hours, when the cell was in continuous operation, it always contained (after 3 hours from the start of operation) one relatively freshly inserted anode which carried a high-current intensity, one anode about half dissolved which carried a reduced current intensity and one anode almost completely dissolved which carried a current intensity near the lower of the limiting values specified above. By continually replacing the anodes, the cell can be run at an average power consumption of 1,000 watts at about 5 volts, i.e. under extremely constant conditions.

It can be seen that using similar designs it is possible, given a larger number of electrodes, to obtain a completely uniform current consumption throughout the cells with any approximation using the same principle. In this case, groups of anodes rather than individual anodes may be used. However, this cell also has disadvantages, the most serious of which is that a fairly complicated mechanism is required for removing the spent anodes and for introducing the new anodes. This is because the complex organometallic electrolyte is highly air sensitive and in some cases is even spontaneously inflammable, so that precautions have to be taken to ensure that air cannot enter the cell when the electrodes are being replaced. Another disadvantage is inherent in the design of the cell. For commercial purposes, the cell naturally has to be increased very considerably in size so that it is able to use, for example, I0,000 to 100,000 a. However, a cell designed on a semicommercial scale which passes a current of about 1,000 a. has itself some deficiencies. These deficiencies result from the relatively low conductivity of the organometallic electrolyte which makes it absolutely essential that the electrode gap should not undergo any appreciable change during the dissolution of the metal anodes. Hence, it is only possible to use anodes which are a few millimeters thick. Although the anodes could be made as thick as desired and the rotating disc cathodes provided with corresponding clearances, the cell would become increasingly uneconomic as it is run. Thus, for example, if anodes mm. thick were used and the electrolysis was started with an electrode gap of 2 mm. on both sides,

the electrode gap would become six times wider during the dissolution of the anode. This in turn would lead to a very large increase in the resistance and to a reduction in both the current absorption and the current density, which seriously affects the economics of the cell's operation.

An object of the present invention is to eliminate these difficulties and to provide a generally applicable and economic electrolysis process using such a cell. Initially, attempts were made to replace the individual rotating disc cathodes with double discs which at the beginning of electrolysis lie close together and act like an individual disc but which, during electrolysis, move apart from one another and the slowly dissolving metal anodes can continued to be introduced so that the gap between anode and cathode remains practically constant. Such an arrangement has the advantage that the anodes need only be replaced infrequently, for example every 24 hours when the anodes are 30 mm. thick. However, this system has the disadvantage that a complicated design of the rotor is needed to enable the interval between the pairs of discs to be adjusted in operation, i.e. during rotation. Further disadvantages include the fact that the individual cathode disc is only active on one side during the greater part of electrolysis and that it is only possible to accommodate in a given space a much smaller number of thick anodes with a correspondingly smaller surface area than thin anodes which are only a few millimeters thick. The overall dimensions of a cell can be made very much smaller for a given current absorption when using thin electrodes. It has also been found in operating such a test cell, with adjustable pairs of cathode discs, that introducing and removing the fairly large and heavy anodes in the complete absence of air is difficult.

An electrolysis cell according to the present invention uses relatively thin metal anodes, but at the same time avoids all the disadvantages of previous designs.

Accordingly, the invention provides an electrolysis cell comprising at least two disc-form cathodes which are arranged vertically in the electrolyte, and at least one sheet-form metal anode and means for introduction of the anode into the electrolyte during electrolysis as it is dissolved by the electrolysis.

When operating a cell according to the invention, the anode material is replenished, as required, from outside the electrolysis cell by directly joining the new anode to the anode which has almost been dissolved. Accordingly, when introducing more anode material, even when the electrolysis is operated for a very long time, it is not necessary to open the cell. Opening the cell usually requires a gate to prevent air from getting in to the cell and the present invention avoids leaks through diffusion or defective operation of the gates.

The invention is further explained with reference to the accompanying drawings in which embodiments of a cell according to the invention are shown by way of example.

FIG. 1 is a schematic showing depicting three phases of the operation of the cathode-anode system of the invention,

FIG. 2 is a schematic representation of a cell according to the invention;

FIG. 3 and FIG. 4 are plan views in cross section of alternative means for mounting of and making electrical connection with, and moving the anodes, in the upper part of the cell, above the level of the electrolyte;

FIG. 5 is a schematic representation of one procedure for connecting a new anode strip to a nearly consumed anode strip; and

FIG. 6 shows a system for automatically feeding a plurality of electrode strips to a cell.

FIG. 1 diagrammatically illustrates a strip of anode material 1 dipping into an electrolyte in the gap between two disc cathodes. For simplicity, the drawing shows only one disc cathode 2 mounted on a rotor shaft 3.

In this example, the cathodes are in the form of circular rotating discs which are wetted with mercury. However, the principle of the invention of introducing anodes into electrolysis cells may also be applied to cathode systems of a fundamentally difi'erent type. The principle of the invention is, however, most readily applied to a cell comprising circular rotating cathodes in the form of discs.

The anode 1 is in the form of a metal band of any length and a few millimeters thick, e.g. about 2 to 6 mm. thick; the width of the band is desirably somewhat smaller than the diameter of the rotating disc cathodes. If such a band, which is initially cut off horizontally, is inserted from above between a pair of rotating disc cathodes, as shown in FIG. 1, phase I, part of the anode is dissolved during electrolysis in the area shown by the hatching in FIG. 1, phase I. This produces, eventually, the situation shown in FIG. 1, phase ll. lf then the band anode is pushed down into the position shown in phase [II of FIG. 1, a substantially sickle-shaped portion is electrolytically cut out of the anode as shown by the hatching in FIG. 1, phase III and eventually is completely dissolved as the feed continues.

The only precaution that must be taken during the feed of the anode is to ensure that the tips of the crescent-shaped part of the anode band never come into contact with the mercury in which the cathode discs rotate. This would immediately result in short-circuiting and with lead anodes would immediately lead to dissolution of the lead in the mercury. Accordingly, a safety clearance of about 0.5 to 1 cm. is desirably left between the lowest points of the lead band and the surface of the mercury.

It is not difficult to calculate or to determine by plane geometry that the crescenbshaped part of the anode band which is dissolved in one stage of the process constitutes about 35 percent of the surface area of the individual cathode discs. However, since the anode is attacked on both sides and the cathode discs are also active on both sides, the surface of the individual cathode disc which is actually effectively used amounts to some 70 percent of the circular area.

If an electrolysis cell according to the invention is to operate reliably, the band anode must satisfy the following requirements:

1. The band must be fixed accurately and firmly between the rotating cathodes;

2. The band should be connected to a source of current at a suitable point, if possible without involving a large resistance in this connection;

3. The fixed hand must be capable of being readily and quickly released both from its position and from the electrical contact with the source of current so that it can be pushed forward a suitable distance;

4. After it has been pushed forward, the band must be capable of being readily fixed in position and quickly brought back into contact with the source of current. Although in theory, simply moving the band by the correct distance, e.g. by hand,

would be possible, it is nevertheless desirable that overflow edge 5 and with an interrupted partition 6 which acts as a support for the band anode.

The cell further includes a tank 9, electrolyte 10 having upper level 11, tank top 12 and cell cover 13. The electrode extends outwardly through the tank top 12 and cell cover 13, through two seals 15 and 16. The tank top 12 and cell cover 13 are jointed together to form a gas space 14, into which an inert gas, e.g. nitrogen, under a positive pressure, i.e. above atmospheric and above the pressure in the cell (which can be atmospheric,) can be introduced via inlet 17. In this manner entry of air into the cell can be prevented.

The anode l is connected to a source of positive potential as indicated at 18; the cathode 2 is electrically connected to the shaft 3 which is connected outside the cell to a source of negative potential as is indicated at 20, via brush 19.

Means for holding and lowering the anode can be disposed in the space 21 between the electrolyte level 11 and tank top 12, such means being shown in FIG. 3 and FIG. 4.

The band anode shown in FIGS. 3 and 4 satisfy these criteria. Each individual band anode l is in contact with a copper plate 7 with which it makes electrical connection. This arrangement is preferably spaced well away from the surface of the electrolyte. Copper plates may also be provided on both sides of the anodes. Inflatable bodies 8 of an elastic material, for example in lenticular or rectangular form, are arranged on both sides of the current-carrying parts, both the anodes and copper plates. Elastic metal bellows or even suitable rubber devices may be used as these inflatable members. Special types of rubber are available that are resistant to the corrosive effect of the electrolyte, which may be sprayed upwards, or of the aluminum alkyls volatilizing from it. It is also possible to use inflatable bodies of vulcanized rubber or of any kind of synthetic rubber which are covered with thin films of polytetrafluoroethylene, polypropylene, poly-4-methyl-lpenetene or of similar polymers which are highly resistant chemically. The device as a whole is accommodated in a shaft of suitable length above the actual electrolysis zone so that at most it will assume a slightly elevated temperature, but will never reach the temperature of the electrolyte itself.

Naturally, a large number of these individual components may be arranged beside each other in a shaft of suitable cross section, i.e. in alternation beginning from the shaft support, inflatable body copper plate lead band copper plate inflatable body copper plate and so on. Small tubes lead from the inflatable bodies to a common pipe through which these bodies can be inflated by suitable means, e.g. by using a gas or oil under pressure. The copper plates which are ex-' tended sideways, are connected with the source of current.

It is not difficult to see how such an arrangement can be operated to fulfill the requirements specified above in points 1 to 5 for the band anode. When the inflatable bodies are flat, the anode bands are first pushed in to the lowest point and then sufficient pressure is applied to the inflatable bodies, thus both fixing the anodes mechanically and making electrical connection. When after a certain period of electrolysis the lower end of the anode has been dissolved, the pressure inside the inflatable bodies is briefly released or reduced. Thus, the band anodes are able to slip spontaneously down on to the previously described cell support under their own weight, being retarded somewhat by friction. The anode band is then fixed in position again by increasing the pressure in the inflata ble bodies.

In practice, a pressure of 0.05 atoms is sufficient to fix the entire system of plates, for example when using a metal band 20 cm. wide and a rubber sac of 16 cm. diameter. The bearing pressure amounts to approximately 10 kg. The difference in voltage between the lead band and the current-carrying copper plate was measured under this load at a current intensity in the individual anode of 60 a. The voltage loss amounted to 30 mv. where the pressure inside the inflatable bodies was 0.05 atoms and to 20 mv. where the pressure was 0.] atom. There was no further change in this value when the pressure was increased. These are extremely good values; and these minimal voltage losses through the resistance of the connection are of no consequence at all when using a total cell voltage of about 4 to 5 volts.

It is even possible to accommodate this device in the shaft above the cell itself with such little clearance that, after the inflatable bodies have been blown up, air is also completely prevented from penetrating from above into the cell. However, this is not nonnally necessary because the exclusion of air can be simply and reliably ensured by other methods. Ac cording to the invention, the band anodes are guided at the upper end of the shaft through a suitable elastic sealing material which prevents air from entering. This sealing system may also be duplicated so that, e.g. two seals are arranged one above the other a few centimeters apart, the gap between the protective plates being placed under a slight pressure of nitrogen.

Although theoretically there are no limits to the length of the band anodes which are used in accordance with the invention, in practice this is not so. Thus, the problem of joining a new anode to the spent anode arises, although this can be overcome without any difiiculties. It is only necessary to meet one requirement, namely that the joining should be completed while the upper part of the dissolving anode in the electrolyte still projects far enough from the cell. The new anode can then be joined on to the old one, for example by welding.

One particularly simple method for providing a continuous feed of the anode would be to install an extruder above the cell. Thus, welding or melting operations could be avoided by joining the replacement anode with the almost exhausted anode using a dovetail joint of the kind frequently used in carpentry. As shown in FIG. 5, the two plates merely have to lie tightly together at the joint, and if necessary may be held together under light pressure. This joint serves its purpose without any danger of traces of the old anode becoming detached and dropping into the mercury when a joint of this kind arrives in the dissolution zone as electrolysis proceeds, cf. FIG. 5.

The invention has been described with reference to a cell in which lead anodes are dissolved, to form, e.g., a tetra-alkyl lead compound. This is a most important application. However, it may also be readily used with other metals. Other suitable anode materials include in particular, tin, antimony, bismuth and aluminum. This method of replacing used anodes would appear to be particularly important in the case of aluminum because greater difficulties are involved in welding this metal than in welding lead.

It is, or course, also possible to use the anodes leading into the electrolysis cell in the form of extremely long bands wound into rolls which may then be fed intermittently into the electrolyte by a suitable mechanism. In cases where bands wound into rolls are used, this can be achieved by arranging the system of rolls one above the other along a slope as shown in FIG. 6. Unfortunately, this arrangement has the disadvantage that the anodes are unable to drop the correct distance under their own weight.

Apart from electrolysis cells, the method according to the invention of letting metal tapes into a reactor in the absence of air may, of course, also be used for other purposes, for example in the production of high-purity aluminum. In this, a system of cathodes is arranged opposite to aluminum anodes inserted into the cell in accordance with the invention, and either a solid high-purity aluminum is deposited on to thin, fixed aluminum cathodes at a low-current density, or alternatively, aluminum is deposited in the form of a crystalline powder at high-current densities, the powder being subsequently discharged from the cell in a continuous cycle using sludge pumps.

The invention is particularly suitable for the production of metal alkyls by the electrolysis of organometallic compounds, in particular, of organic aluminum compounds of the type described in German Pat. specification No. 1,161,562. This patent specification relates to the production of alkyl compounds of lead in particular, but also of other solid metals such as magnesium, aluminum, tin, antimony or bismuth. In this process, an electrolyte containing a compound of the general formula M (AlR R') in which R represents an alkyl radical, R represents an alkyl-, alkoxyor aroxy radical which may be substituted or fluorine and M represents sodium, potassium or mixtures of sodium and potassium, is electrolysed on anodes of the above metals and a mercury cathode. The process is particularly suitable for the production of organometallic compounds containing alkyl radicals with up to six carbon atoms, the production of lead tetra-alkyl compounds being a particularly important commercial application. The lower lead tetra-alkyls which are extensively used in practice, in particular lead tetramethyl and lead tetraethyl, may be produced with advantage in accordance with the invention using the principles discussed earlier on.

So far as the general chemistry of this manufacturing process is concerned, attention is drawn in particular to German Pat. specifications No. l,l66,l96 which relates, for example, to the production of tetraethyl lead by the electrolysis of organic aluminum complex compounds, and to No. l,220,855 relating to the corresponding production of lead tetramethyl. Other important information on the production of metal alkyls by electrolysis and hence on the potential applications of the invention may be found in German Pat. specifications Nos. l,l50,078 and 1,157,622. The first of these two patent specifications relates to the production of aluminum trialkyl and magnesium dialkyls in the presence of organic aluminum complex compounds as electrolytes, whilst the second relates to an important modification for the production of lead tetramethyl through the electrolysis of organic aluminum complex compounds in particular.

We claim:

1. An electrolysis cell for electrolysis of an electrolyte containing an organo aluminum alkyl of the formula M(AIR,R) in which R is alkyl, R is alkyl, alkoxy, aroxy or fluorine, and M is sodium, potassium, or a mixture of sodium and potassium between an anode of lead, aluminum, tin, antimony or bismuth and a mercury cathode for production at the anode of alkyl compound of the metal of the anode, comprising:

a. an hermetically sealed tank for the electrolyte,

b. a container for holding the mercury cathode disposed in the bottom of the tank,

c. at least two spaced, parallel, disc-form plates rotatably mounted and disposed vertically in the tank partially dipping into the mercury container, said plates being connected to a source of negative potential,

d. a strip-form anode disposed vertically in the tank between the disc-form plates, extending upwardly through the top of the tank and connected to a source of positive potential,

e. and anode feed means for controlled advancing of the anode between the cathodes to compensate for dissolving of the anode by the electrolysis.

2. A cell as claimed in claim 1, including a bath of mercury in the mercury container, and means maintaining the electrolyte tank filled to at least adjacent the top of the disc-form plates, the anode terminating above the mercury.

3. A cell as claimed in claim 51, 'n which a partition is disposed between the disc-form plates for supporting the anode and preventing the anode from touching the surface of the mercury.

4. A cell as claimed in claim 3, said anode feed means including selectively releasable holding means for keeping the anode in a fixed position in the cell and selectively releasing the anode for said advancing thereof, the anode being able to advance into the electrolyte under gravity when the holding means is released.

5. A cell as claimed in claim 4, including a bath of mercury in the mercury container, and means maintaining the electrolyte tank filled to at least adjacent the top of the disc-form plates, the anode terminating above the mercury.

6. A cell as claimed in claim 1, said anode feed means including selectively releasable holding means for keeping the anode in a fixed position in the cell and selectively releasing the anode for said advancing thereof.

7. A cell according to claim 6, the anode including, without the cell, a rolled portion from which the anode can be fed to the cell.

8. A cell as claimed in claim 6 in which the anode is able to advance into the electrolyte under gravity when the holding means are released.

9. A cell as claimed in claim 6 in which the holding means comprise an inflatable body which when inflated presses against the anode and holds it in position.

10. A cell as claimed in claim 9 in which the inflatable bodies are lenticular or rectangular sacs of material which is inert to the electrolyte.

11. A cell as claimed in claim 6, and switch means in said connection of the anode to a positive potential, said holding means being effective to close said switch when holding the anode in place and open said switch when the anode is released by the holding means.

12. A cell as claimed in claim 6, in which the holding means comprise an inflatable body which when inflated presses said connection of the anode to a positive potential, said holding means being effective to close said switch when holding the anode in place and open said switch when the anode is released by the holding means, said switch comprising a metal strip interposed between the anode and the inflatable body.

13. A cell as claimed in claim 12 in which the metal strip is made of copper.

14. A cell as claimed in claim 1, and a second seal for the anode.

15. A cell as claimed in claim 1, and a second seal for the anode disposed outside the tank, and means for maintaining a gas inert to the electrolyte under positive pressure between said seals, preventing air from entering the tank.

16. A cell as claimed in claim 1 in which the strip form anode comprises a strip which is joined outside the tank to a new strip of anode material.

17. A cell as claimed in claim 16 in which the anode strips are joined by a dovetail joint.

18. A cell as claimed in claim 16 in which the anode strips are joined together by welding.

19. A cell as claimed in claim 1 in which the anode is lead.

20. An electrolysis cell comprising:

a. a tank for electrolyte,

b. at least two disc-form cathodes arranged vertically in the tank and connected to a source of negative potential,

c. a sheet form anode disposed vertically in the tank between the disc-form cathodes, extending outwardly of the cathodes, and connected to a source of positive potential,

d. anode feed means for controlled advancing of the anode between the cathodes to compensate for dissolving of the anode by the electrolysis, said anode feed means including selectively releasable holding means for keeping the anode in a fixed position in the cell and selectively releasing the anode for said advancing thereof, and

e. said holding means comprising an inflatable body which when inflated presses against the anode and holds it in position.

21. A cell as claimed in claim 20 in which the inflatable bodies are lenticular or rectangular sacs of material which is inert to the electrolyte.

22. An electrolysis cell comprising:

a. a tank for electrolyte,

b. at least two disc-form cathodes arranged vertically in the tank and connected to a source of negative potential,

c. a sheet form anode disposed vertically in the tank between the disc-form cathodes, extending outwardly of the cathodes, and connected to a source of positive potential,

d. anode feed means for controlled advancing of the anode between the cathodes to compensate for dissolving of the anode by the electrolysis, said anode feed means including selectively releasable holding means for keeping the anode in a fixed position in the cell and selectively releasing the anode for said advancing thereof, and

e. switch means in said connection of the anode to a positive potential, said holding means being effective to close said switch when holding the anode in place and open said switch when the anode is released by the holding means.

23. A cell as claimed in claim 22, in which the holding means comprise an inflatable body which when inflated presses against the anode and holds it in position, and switch means in said connection of the anode to a positive potential, said holding means being efiective to close said switch when holding the anode in place and open said switch when the anode is released by the holding means, said switch comprising a metal strip interposed between the anode and the inflatable body.

24. A cell as claimed in claim 23 in which the metal strip is made of copper.

2272 8;? v. UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO. 3,620,954 Dated Nov. 16, 19?;

Inventor) Karl Ziegler et a1.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

r- Col. 1, .rline 22, change "cross-section" to "current".

Col. 4 lines 13 and 14 correct the spelling of "poly-4-methy1-l-pentene" Col. 8, lines 27-28, cancel "and switch means in said connection of the anode to a positive potential,"

Signed and sealed this 20th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER ,JR. ROBERT GOTTSCHALK Attesti ng Officer Commissioner of Patents 

2. A cell as claimed in claim 1, including a bath of mercury in the mercury container, and means maintaining the electrolyte tank filled to at least adjacent the top of the disc-form plates, the anode terminating above the mercury.
 3. A cell as claimed in claim 51, in which a partition is disposed between the disc-form plates for supporting the anode and preventing the anode from touching the surface of the mercury.
 4. A cell as claimed in claim 3, said anode feed means including selectively releasable holding means for keeping the anode in a fixed position in the cell and selectively releasing the anode for said advancing thereof, the anode being able to advance into the electrolyte under gravity when the holding means is released.
 5. A cell as claimed in claim 4, including a bath of mercury in the mercury container, and means maintaining the electrolyte tank filled to at least adjacent the top of the disc-form plates, the anode terminating above the mercury.
 6. A cell as claimed in claim 1, said anode feed means including selectively releasable holding means for keeping the anode in a fixed position in the cell and selectively releasing the anode for said advancing thereof.
 7. A cell according to claim 6, the anode including, without the cell, a rolled portion from which the anode can be fed to the cell.
 8. A cell as claimed in claim 6 in which the anode is able to advance into the electrolyte under gravity when the holding means are released.
 9. A cell as claimed in claim 6 in which the holding means comprise an inflatable body which when inflated presses against the anode and holds it in position.
 10. A cell as claimed in claim 9 in which the inflatable bodies are lenticular or rectangular sacs of material which is inert to the electrolyte.
 11. A cell as claimed in claim 6, and switch means in said connection of the anode to a positive potential, said holding means being effective to close said switch when holding the anode in place and open said switch when the anode is released by the holding means.
 12. A cell as claimed in claim 6, in which the holding means comprise an inflatable body which when inflated presses against the anode and holds it in position, and switch means in said connection of the anode to a positive potential, said holding means being effective to close said switch when holding the anode in place and open said switch when the anode is released by the holding means, said switch comprising a metal strip interposed between the anode and the inflatable body.
 13. A cell as claimed in claim 12 in which the metal strip is made of copper.
 14. A cell as claimed in claim 1, and a second seal for the anode.
 15. A cell as claimed in claim 1 and a second seal for the anode disposed outside the tank, and means for maintaining a gas inert to the electrolyte under positive pressure between said seals, preventing air from entering the tank.
 16. A cell as claimed in claim 1 in which the strip form anode comprises a strip which is joined outside the tank to a new strip of anode material.
 17. A cell as claimed in claim 16 in which the anode strips are joined by a dovetail joint.
 18. A cell as claimed in claim 16 in which the anode strips are joined together by welding.
 19. A cell as claimed in claim 1 in which the anode is lead.
 20. An electrolysis cell comprising: a. a tank for electrolyte, b. at least two disc-form cathodes arranged vertically in the tank and connected to a source of negative potential, c. a sheet form anode disposed vertically in the tank between the disc-form cathodes, extending outwardly of the cathodes, and connecteD to a source of positive potential, d. anode feed means for controlled advancing of the anode between the cathodes to compensate for dissolving of the anode by the electrolysis, said anode feed means including selectively releasable holding means for keeping the anode in a fixed position in the cell and selectively releasing the anode for said advancing thereof, and e. said holding means comprising an inflatable body which when inflated presses against the anode and holds it in position.
 21. A cell as claimed in claim 20 in which the inflatable bodies are lenticular or rectangular sacs of material which is inert to the electrolyte.
 22. An electrolysis cell comprising: a. a tank for electrolyte, b. at least two disc-form cathodes arranged vertically in the tank and connected to a source of negative potential, c. a sheet form anode disposed vertically in the tank between the disc-form cathodes, extending outwardly of the cathodes, and connected to a source of positive potential, d. anode feed means for controlled advancing of the anode between the cathodes to compensate for dissolving of the anode by the electrolysis, said anode feed means including selectively releasable holding means for keeping the anode in a fixed position in the cell and selectively releasing the anode for said advancing thereof, and e. switch means in said connection of the anode to a positive potential, said holding means being effective to close said switch when holding the anode in place and open said switch when the anode is released by the holding means.
 23. A cell as claimed in claim 22, in which the holding means comprise an inflatable body which when inflated presses against the anode and holds it in position, and switch means in said connection of the anode to a positive potential, said holding means being effective to close said switch when holding the anode in place and open said switch when the anode is released by the holding means, said switch comprising a metal strip interposed between the anode and the inflatable body.
 24. A cell as claimed in claim 23 in which the metal strip is made of copper. 